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I live in Washington, and travel around the Pacific Northwest often. It's a beautiful environment, full of huge plains of grass with (virtually) nothing in them.

I was wondering if, in order to help combat climate change, I (and a lot of other people) engaged in "Guerilla Gardening". According to these pages, one tree sucks up ~12 tons of CO2 over its lifetime[1], and 1 ppm is equal to 2B tons[2].

By this logic, in order to go from 400 ppm -> 300 ppm, we would need to plant about 16B trees. While this seems like a very large number, you could have large numbers counteract it (e.g. rally 1M people over 20 years). The problem is where to go about it - this is where guerilla gardening would come in.

What if whenever I saw one of these huge plains, I stopped, jumped out of my car, threw 20 (locally flora appropriate) seeds in the ground, and drove on. Would that work? Would that violate some property/state/federal issue? Would it help?

[1] http://learn.eartheasy.com/2014/01/10-carbon-storing-trees-and-how-to-plant-them/

[2] https://www.skepticalscience.com/print.php?r=45

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    Those grass plains probably have lots of stuff in them. They are prairie ecosystems, and store lots of carbon in root mass & soil humus. There are probably good reasons why they don't have trees already, such as insufficient ground water, grazing, &c, so dropping a few seeds is not going to do anything much. After all, many tree seeds have mechanisms that enable them to spread for long distances.
    – jamesqf
    Jul 14, 2015 at 18:12
  • An interesting separate question would be if (and what kinds) of forest store more carbon than grasslands. Also if there's a biome that reliably sequesters carbon for a longer timespan.
    – mart
    Jul 15, 2015 at 12:33

2 Answers 2

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I think you're up against two three at least four separate problems:

  1. The scale: rallying 1M people to plant 16k trees apiece over 20 years is no way a "guerrilla" operation; it's a mass movement. It won't be covert: everyone will know about it, and landowners will probably object more or less strenuously.
  2. The distribution: if you have anywhere near 1M people randomly scattering seeds about, you'll find that there will be piles of seeds near the obvious places (highway rest stops, obvious side roads, etc) and nothing elsewhere. Without coordination, you'll never get the acreage covered.
  3. The planting: as noted by @jamesqf, prairies are prairies not just because they have never seen tree seeds, but because they're stable ecosystems. Without some tending, the trees are unlikely to get started, and even then they may not last.
  4. And, as noted by @jamesqf, disturbing a stable ecosystem that's been capturing carbon for a long time probably isn't a good way to rally against climate change.
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    I was reminded of this question not too long ago, and I agree with all the points EXCEPT #3. While this is the case for many plains, I think lots and lots of these plains are empty because of settlers who cleared them during the expansion of America in the 18th, 19th & 20th centuries. I'm not saying this undoes the other issues, but, in some ways, it is an opportunity to revisit what is "natural".
    – aronchick
    Mar 25, 2020 at 21:07
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Your calculations are way off.

One cubic meter of wood harvests about 1 tonne of carbon dioxide.

An average tree is 0.6 cubic meters so that's 0.6 tonnes of carbon dioxide per tree.

To reduce atmospheric carbon dioxide from 400 ppm to 300 ppm, you need to remove 777 gigatonnes of carbon dioxide. Your calculation was that 192 gigatonnes would be enough but it's not. Perhaps you are confusing gigatonne of carbon dioxide with gigatonne of carbon? There's 3.66x difference between those.

That's 1300 billion trees required. Not 16 billion.

It would be about 168 trees per person.

Where would you find enough land area for all those trees?

Edit: on second thoughts, assuming 720 trees per hectare, converting 36% of all agricultural land area (which is 5 billion hectares) to forest would be enough to eventually (after 100 years) reduce carbon dioxide concentration from 400 ppm to 300 ppm. However, you'd have to kill 36% of world population first. Or maybe they die because of starvation after implementing the plan as there won't be enough food for them. Well, on a more positive side, if meat consumption would decrease drastically (for example by artificial lab-grown meat becoming less expensive), then maybe we could achieve 36% agricultural land area reduction.

...or maybe it's too optimistic to assume an average tree is 0.6 cubic meters as that would give 720 trees per hectare * 0.6 cubic meters per tree = 432 cubic meters per hectare which to me as a forest owner seems way too optimistic. You can achieve maybe half that by letting your forest grow very old. So maybe 720 trees per hectare is counting all trees, including very small ones, not just large trees. So better make 36% agricultural land area reduction into 72% agricultural land area reduction. I'm not sure we can realistically achieve that, unless each and every person on this planet stops 100% of meat consumption immediately. There won't be enough land.

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  • The obvious answer is by storing fully grown trees somewhere. That lets us re-use the same bit of land multiple times. And grass might be better than wood since it grows faster. Under the sea is probably easiler than the more traditional underground, at least on the timescale we care about right now. Piling them on a subduction zone is all very well, geologically speaking, but making landfills on lowlying coastal areas that are going to get inundated soon is quuicker and has other uses.
    – Móż
    Jun 29 at 23:37
  • Atmospheric CO2 has recently risen to 500 ppm. i guess the 1000 + trees I planted aren't working. Jul 1 at 15:58
  • Man, for better or worse, there is SO much land out there. I could plant 168 seeds in an afternoon just driving to Mt. Baker
    – aronchick
    Jul 1 at 18:34

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